The present invention relates to an image forming method by which a continuous gradation recording is conducted on a silver halide photographic material.
Conventionally, the importance of gradation is well known in order to reproduce a high quality image. Stating gradation more concretely, the continuity in continuous gradation, in particular, the reproduction of low density gradation in portions in which the density is almost uniform, such as the moderate gradation in the contrast in the skin of an enlarged human figure or in the sky is very important. In order to realize good gradation in a digital image, gradation control higher than at least 200 levels is requested. On the other hand, a technique to record a continuous gradation image with an array light source is well known. The array light source makes it possible to conduct image formation at high speed and at low cost with a small sized apparatus.
For example, the following methods are well known.
(1) A first method such as the Dither method with which a multi-gradation image is depicted in the pseudo sense by combining a plurality of binary pixels.
(2) A second method with which the light intensity or the light emission time period per one time of each element in the array light source is changed independently in accordance with the gradation level. However, since the first method is a pseudo-depiction method in which the image resolution is sacrificed, it may be difficult to expect high resolution recording. With the second method, a D/A converter and a comparator are needed for each recording element, resulting in a driver circuit for the recording elements which becomes complicated and expensive.
Then, a third method with which a multi-level recording is conducted by plural time exposures with the use of a binary or multi-level array light source may be considered.
However, with the third method, good gradation may be obtained without degrading the resolution and without causing the apparatus to become complicated and expensive. On the other hand, in the condition that the gradation is enhanced, there may be a problem that density unevenness caused by the deviation among the light emission characteristics of each recording element becomes conspicuous.
To overcome this problem, the following correction may be considered. That is, the recording elements are controlled sequentially one by one to emit light and the emitted light intensity of each element is measured, the correction value for the deviation among the light emission characteristics of each recording element is obtained on the basis of the measurement, and the correction is conducted on the basis of the correction value. For example, in the method disclosed in WO90/09890, since recording is conducted on a recording medium of a high contrast gradation characteristics, the gradation depiction is conducted basically only by area modulation, it may be difficult to obtain a sufficiently continuous gradation image. To counter this problem, a technique to improve the gradation continuity with the use of a line-formed light source element with which the recording width per one line is made small may be considered. However, on the other hand, it is difficult to obtain the maximum density due to the deficiency of the light amount, resulting in another problem being raised. Further, in the case of the application on a silver halide photosensitive material of the low contrast recording medium, the recording mode shows the density modulation and the continuous gradation is enhanced. However, since the density unevenness may not be eliminated appropriately, there may another problem in that the unevenness on the portion in which the density is almost an equal density which is especially important for the reproduction of the gradation becomes conspicuous in comparison with a complicated image portion.